Re: object handling

["Brett Bibby" <research@...>]

Thanks for the info, really helpful.  How can I get lua to garbage
collect functions?  Over time as I run more and more functions, some
become unneeded.  Is there any way to get rid of these?
Brett

----- Original Message ----- 
From: "Kevin Baca" <lualist@aidiastudios.com>
To: "'Lua list'" <lua@bazar2.conectiva.com.br>
Sent: Wednesday, October 15, 2003 10:40 PM
Subject: RE: object handling


> Yes.
>
> Also, check out the __gc metamethod.  With it you can do the converse.
> When a lua object is GC'd you can then delete the C object.
>
> -Kevin
>
> >
> > Kevin,
> > That's very helpful, thanks.  If I call a functin that
> > deletes an object in my engine, can I then delete the table
> > (e.g.A123) by setting it to nil? Thanks again, Brett
> >
> > ----- Original Message ----- 
> > From: "Kevin Baca" <lualist@aidiastudios.com>
> > To: "'Lua list'" <lua@bazar2.conectiva.com.br>
> > Sent: Wednesday, October 15, 2003 10:09 AM
> > Subject: RE: object handling
> >
> >
> > > To pass the table A123 to a lua function from C:
> > >
> > > //Retrieve the lua function
> > > lua_pushstring( L, "funcname" )
> > > lua_gettable( L, LUA_GLOBALSINDEX );
> > >
> > > //Retrieve A123 (assuming it is a global)
> > > lua_pushstring( L, "A123" )
> > > lua_gettable( L, LUA_GLOBALSINDEX )
> > >
> > > lua_call( L, 1, 0 ) //call funcname() with 1 arg and 0 return vals
> > >
> > > Some other things to think about:
> > >
> > > You could have a lua function create the lua table and the C
object
> > > simultaneously, then store a reference (userdata) to the C object
in
> > the
> > > lua table.
> > >
> > > Conversely, create the lua table and the C object
> > simultaneously from
> > C
> > > and store a reference to the lua table in the C object
> > (perhaps using
> > > the lua_ref() macro).
> > >
> > > Or you can mix and match as you desire.
> > >
> > > Either way, once you have a way to create objects you might want
to
> > > think about defining all object variables (C-side and
> > lua-side) in lua
> > > because lua provides such a nice syntax for that sort of thing.
> > >
> > > Example:
> > >
> > > -- This creates a new tank object that contains a reference
> > > -- to a C object (as a userdata)
> > >
> > > function Tank( tankDef )
> > >     local tank =
> > >     {
> > >         ammo = tankDef.ammo,
> > >         health = tankDef.health
> > >     }
> > >
> > >     -- Create the C object (a userdata) and store a ref to
> > >     -- it in tank.__cobj__
> > >     tank.__cobj__ = C_tankCreate( tankDef.actorData )
> > >
> > >     return tank
> > > end
> > >
> > > -- The following will call Tank() and tank0 will
> > > -- refer to the new tank
> > >
> > > tank0 = Tank
> > > {
> > >     ammo = 10,
> > >     health = 100,
> > >     actorData =
> > >     {
> > >         -- Internal C data
> > >         followTerrain = true,
> > >         collideable = true,
> > >     }
> > > }
> > >
> > > This way you can define lua-side data and C-side data in in the
same
> > lua
> > > config table.
> > >
> > > Hope that makes sense.
> > >
> > > -Kevin
> > >
> > > > Newbie question....
> > > >
> > > > We're trying to come up with an efficient way to handle our game
> > > > objects from lua.  For a given game object, we define a complete
> > > > schema that includes the engine data and the game
> > extensions to that
> > > > data.  So for example, an Actor schema will have some
> > core internal
> > > > use variables and some additional game specific variables
> > (e.g. tank
> > > > might have armor, player might have health, etc.)  Currently, we
> > > > stuff the engine's internal variables into a C struct and the
> > > > additional variables into a lua table, then use lua bindings
> > > > to call engine functions that operate on the internal data
> > > > and use lua directly to manipulate the lua tables. So far so
good.
> > > >
> > > > At authoring time all of this is transparent to the
> > designer.  They
> > > > simply create instances of actors and add new variables
> > to them as
> > > > they need them.  When they export the game, we split the data
and
> > > > generate a guid for each engine object and embed that in
> > the engine
> > > > data and then create a lua table with the same name as
> > the guid that
> > > > also contains elements to hold the additional variables.
> > > >
> > > > My questions are:
> > > >
> > > > 1.  Is this a lame way to do this?  What are the other
> > ways? (either
> > > > implicitly or explicitly) 2.  If I have a guid of A123
> > (stored as a
> > > > 4 byte int, not char) and I create a lua table as A123 =
> > {}, when I
> > > > call from the engine into lua, what do I need to pass lua (or
> > > > configure before calling) so that a lua funciton can receive the
> > > > correct table to operate on?  I tried several experiments
> > passing in
> > > > the A123 as a number and a string and it doesn't work.
> > Do I need to
> > > > pass the table itself?  How do I do that?
> > > >
> > > > Thanks for the help.
> > > > Brett
> > > >
> >